Hot-wire electric measuring instrument.



o. SGHBMANN. HOT WIRE ELECTRIC MASURING INSTRUMENT. APPLGATION FILED MAY 6, 1911 gmgm mam Feb. 23, 1915.

Hagi

DE? HARTMANN a BRAUN, iL-G.,

OTVIE ELECTRIC MEASURING NSTBUBIENT.

ppieation filed may S, 1911.

To @ZZ 11:72am may; concern e it lmown thai l, OSCAR Senmdim. a citizen of ehe German Empire. and resid4 moe of Hesse-Nassau and Kingdom oi Prue sin, Germany, have inventedeertain new and useful improvements in Hot-Wire Electrio Measuring Instruments, of which the following is a specification.

-Ho Wire :immer-ers of the type commonly used are for several reasons unsuitable for hignrequency currents. One of ehe mein reasons of such nnsnitability is the neces* sity of subdiriding die hoiewiro by means oi silver strips forming current loops, the influence of 'which varies with the frequency of the current, These inconveniences are especially met Wih in high intensities, where it is not possible to use ordinary shunts; since the ratio o1" resistance or of conduct" .ity of both materials-wire and shunt-ls subject. to considerable alterations.

The. present invention has -for its objee to sui-mount hese diiiiculties by carrying the current inlensity through one parli or several nahs of current arranged rectilinealljyv so as 'lo .form no loop whatever. Hilherto wires have been employed of great lengeli possible with relation lo he size of the in .aiment box-l5 to 2li em. long; bul expe ienre .has proved, iiiui such Wires are noi sniiable for the oui-pose in question.

l'egarding the inereia or' lie adjustment, lne cross section of the hot-wire should no*v exceed a eerlain size about Chl inni. sana el Owing lo the total current fr ihren i ine long hol-wires of 11n-ii ite/,l insru.-

ments. a great heating results. ni-cessitaing complicated eontriranees for Conil-)ensuring the eli'eels thereof, resulting in lhe 'ly occurrence of lfauls in the poinler adiestment.

lVhile the invenion is necessarily susceptible oi structural-'modifiation u'ithonlt departingy from. rhe spirit or scope thereof, a preferable and practical form of construction is shown in he accompanying dran'- ngs, in which- Figure l is a lop plan View, partij/'an d1agram olE a ho-wire ammeerembodying he improvement coneniplaed by thepresent invention. Fig. is a vertical cross sectional View of he instrument shown in I* 1g.

Specicaion of Letters Patentl lng' ai. Franlifort-oirtheliain, in the Fresu' serial 625,657.

l, the line of section being laken ai one side ol and excluding the pointer mechanism.

According to he present invention, and

that of the measuring wires hitherto used in4 iiisrumenls for usual sizes. By reason, nevertheless, oi the considerable heating produced in the ribbon. lie elongation or' this short piece can be used for the morenient of the poiner With sullieient accuracy for technical measurements. The ribbons nsed are or" such rirriing thickness, that no Change in conductivity can be observed within very vulde frequencies.

l he heal proflncel i i charaeier tha lll-e hitherto used clamping derives of comp "itirely small metal masses haw noi piord suiable, since they were not able lo radiale the excessive heat with sulli ent rapidity. `rlhis inconvenience is obxiae-'l by r ng stout blocks ol good hea-ronfglnetiriy. These blocks may be eillier eubical or--i` a symmetrical arrangen nient oi the ribbons be` prefer edeylindri ral: lle ribbons being distributed at equal r: orer the cylinder surface. Snell ori'er ihe 'l'iirher advantage that the device can be made extremely `one and immovable., a requirement which sizensable with such uniisi allj,7 shorl if'es. as coinpared'wilh hot-Wire instruriienjs or the usual jfpe wherein long Wires are used with a relatively small radiaion of The cooling ell'eel of the air on the surfaces of the ribbons and the clamping blocks is of such character hat die spende lod of current passing through llie ribbons can be taken niueh higher than in ordinary liotvfvire instruments'hitherto used.

.ln many enses the compensation of the liotArires in relation to the external temperature may be dispensed with since, by reason oli' die g'. at l et produced in the ribbons on the passage of the current, the exernal temperature may be neglected, lloreorer, the problem of devising a compensalion which 'would not prejudiciall' aeet the electrical properties of the system would entail such serious construe tional dieulties that the above mentioned lnileerl of suc-h 'a .estonien een. ier-5.

ranges of lonv and high.

system, perature 'spread over solidity of the 4clamping pieces miffht be compromised. On. the other hand, this solidity may be increased by connecting the clamping blocks with a supportin bridge b, the blocks being kept at equal istances from one another. This is the more necessary seeing that the large current conductors entering at p, p may occasionally, exert a strong distorting influence on the blocks.

It is advisable to form the base plate B to which the blocks are attached of a material `which has nearly the same coellicient of expansion as platino-iridium (as preferably used in hot-Wire instruments for high frequency currents) as for example marble. Though the employment of marble in connection with Zhot-wire instruments is already known, it offers in the present case the special advantage of allowing the bridge b to be made of one material solely, (that is to say notof an alloy) preferably' iron, which has nearly the same coefficient of expension as marble. By arranging the bridge b, which is of course electrically insulated from the heat-radiating blocks in any conventional manner, distortions olf-the active which, owing to variations of tem- Would -gradually develop and the whole instrument., are p'revented.

As the construction herein described does.

not provide for compensating any mechanioa'l yalteration of the ribbons by adjusting the clamping blocks, the correction of the nibbans is dispensed with and any undesirable v'variation in length is neutralized by varying the -which is suitably connected with a movable correcting device al', as shown infFig. l of the drawing. This correcting device may be or" any approved construction, but for illustrative purposes is shown. in the drawings as consisting of an adjustment lever e having a spring or equivalent supporting fulcrum f, and to one end of which lever is attached one end of the bridge wire d, and the other end of whichlever is engaged by an adjusting set screw g having a sullicient delicate adjustment topi-Ovide for the necessary correcticn in the length of the bridge Wire whenever such correction is necessary.

Though various forms of connectors may be ,utilized for connecting the bridge Wire with the pointer device, an illustrated form ot construction is shown in the drawings as consisting of a flexible connector h', Whose terminals are respectively engaged at one end, as at e', with? the bridge .vire al, and at fits other end as at y' with a tension spring 7c. An intermediate portion of the flexible connector h is coiled about the pointer arbor Z, as indicated at m, said pointer arbor carrying the pointer n. which swings over the usual scaled dial (omitted for the salte of elearness).

length of the bridge-Wire d,

As already indicated, a distinctive feature of the present invention, which involves a radical and important departure in the art, resides in the employment ofa hot-strip or strips (wires or ribbons) possessing the dimensional characteristic of not only being o'a very short length, but also exceedingly thin, and to combine such a strip or strips With relatively large heat absorbing or heat radiating blocks of good heat conductivity, as for instance afforded by large blocks of iron. This combination is sharply distinguished 'from the ordinary hot-wire instruments of the usual-type wherein long Wires are used with a relatively small radiation of heat, whereas according to the present invention the cooling elect of the air on the large surfaces of the vthin ribbons, and on the large suracesof'the clamping blocks, provides an arrangement wherein the spec'ifie load of- -current passing through the hot strip-'or-strips-can be taken much higher than in the ordinary hot-Wire strips having the usual long hot-Wire, with relatively small terminals.

It has already been pointed out that the invention also dispenses with, the usual shuntsA which Vhave heretofore been found to be indispensable'in any reliable hot-wire instrument having a long hot-Wire or strip. According to the present invention; the use pf a shunt, with its attendantcomplications, is entirely avoided, and instead thereof, where the current value requires it, a number ot thin strips may be advantageously and conveniently utilized, in parallel, to give the increased capacity for 'carrying the current, but since each'strip or ribbon is alike structurally and functionally it is only necessary to connect the bridge `svire with one of such stri-ps or. ribbons. In further explanation of this feature of the invention, that is utilizing either a single hot strip -or a plurality of such strips, which are usually made of a recious metal, the following dimensional eatures are to be noted, that is to my, if the service `current is of' such strip will not stand it. a plurality of such hot strips is used. These must be extremely thin-about 1./100 mmf-owing to the eddy currents occurring with high frequencies. Besides, they must not be too long lest they are overheated in the center, While the specific load cannot be forced too high. ln order to secure the proper bending effect, the strips must be chosen of particular width. For intensities from 2 up to 5 amp.' e. g., one strip ot some few millimeters width Will do, While for larger currents a plurality of such strips mustbe employed, preferably arranged on a cylinder or block of square section.

A further distinguishing feature of this invention resides in, the 'fact that the novel a value that a single hot iaeeaae tion, and it will, of course, be understood that.

changes in the form, proportion, and minor details of construction as fall -Within the scope of the appended claims, may be re sorted to Without departinglfrom the spirit or sacrificing any oi' the advantages of the invention.

What l claim is:

l. A hot-wire measuring instrument including a casing, a pair of relatively large supporting blocks of good-heat conductivity, and a hot-strip of relatively small length clamped to and extending between said blocks.

Q. A hot-Wire measuring instrument including a casing, a pair or' relatively large supporting blocks of good heat-conductivity, and a hot-strip in the torni of a thin ribbon of relatively small length clamped to and extending between said blocks.

3. A hot-Wire measuring instrument including a casing having a marble base, a pair ot' relatively large supporting blocks of good heat-conductivity, and a hot strip of relatively small length clamped to and extending between said blocks.

vl. A hot-wire measuring instrument including a casing, a pair of relatively large supporting blocks ot' good heat-conductivity, a bridge rigidly connecting the said blocks, and a liot strip of relatively small length clamped to and extending between said blocks.

5. A hotwire measuring instrument inclnding a casing, a pointer device, a pair of relatively large supporting blocks of goed heat-conductivity, a hot strip of relatively small length clamped to and egtending be-V tween said blocks, a bridge wire connecting with the hot strip and also with the pointer device, and an adjustable correcting device connecting with one end or" the bridge Wire.

(S. A. hot-wire measuring instrut'nent including a pair of relatively large siipporting blocks of good heat-conductivity having Wire terminal connections therewith, a series of hot strips of relatively small length arrangedin parallel and clamped to and extending between said blocks, and a pointer mechanism including a bridge wire connection with one oi the h'ot strips.

7. A. hot-wire measuring instrument in cluding a casing, a pair ot' relatively large supporting blocks of good heat-conductivity arranged in the casing and having wire terminal connections therewith, said blocks being of circular form, a: series of hot strips circularly arranged in parallel about the said blocks and clamped to and extending between the same, the said strips being of relatively small length, and a pointer mechanism connecting With one ot the strips.

8. A hot-wire measuring instrument including a casing, a pair of relatively large supporting blocks of good heat-conductivity, a plurality of hot strips clamped to and extending betWeen said blocks, eachof said hot strips consisting of a thin ribbon oi' metal of relatively small length, a pointer mechanism including a bridge wire connection with one of the strips, and an adjustable correcting device connected With one end of the bridge wire. l

ln testimony whereof I have aihxed my signature in presence of two witnesses.

OSCAR SCH-UMANN. lVitnesses 'y JEAN GRUND, CARL GRUND. 

